It is well known to combine electric motors with pump units. In the referenced German Pat. No. 15 38 715, Laing, a combination pump-motor is described in which the air gap is part-spherical, defined by a rotor of part-spherical shape which is surrounded by a stator. The stator is made in form of a lamination assembly which is bulky since the lamination stack or package which results is comparatively large. The combined unit, thus, has a poor space factor and requires substantial material quantity.
It has also previously been proposed to construct a pump-electric motor combination in which the stator is formed of a strip of sheet metal which is edge-wound and formed with winding grooves. Adjacent windings of the edge-wound strip define frusto-conical surfaces. This arrangement has a disadvantage that edge-winding of electrical sheet steel is difficult, resulting in deformation of the sheet steel as it is being edge-wound, which can be overcome only by compressing the sheet steel package, under extremely high pressures. Even high force compression cannot totally eliminate wrinkles and the like which occur along the inner circumference of the edge-wound strip, resulting in undesired air gaps to permit escape of material at the inside of the strip between the electrical sheet steel elements of the stator structure.